1. Field of the Invention
This invention relates to photographic cameras.
2. Description of the Prior Art
Recently, in order to shorten the distance between a photo-taking lens optical system and a film exposure position where a film is arranged for exposure purposes, a plurality of reflection mirrors is arranged between said photo-taking lens optical system and said film exposure position so that an image bearing beam of light rays entering through the photo-taking lens optical system is subjected to successive deflections by the plurality of reflection mirrors in a zigzag manner, thereby shortening the distance between the photo-taking lens optical system and the film exposure position.
This kind of mirror system can be widely found particularly in photographic cameras capable of developing the film upon the pulling-out of the exposed photographic film from the camera, during the pulling process to provide a positive image, or in the so-called "instant photographic cameras".
What is considered as a reason why this instant photographic camera generally requires this type of optical system is that the image formed on the photographic film which is used in the instant photographic camera is the same size as the finished positive photograph, as opposed to the image on the photographic film which is used in the usual camera, where only a negative image is made on said film and this negative image is enlarged to form a positive image in another printing paper. If the size of instant type of film is too small, therefore, the finished photograph is difficult to appreciate. Such instant film is therefore made large, as compared with a roll film of 35 mm size. Therefore, on the instant film, a large image must be projected so that the distance between the photo-taking lens optical system and the film exposure position must be increased sufficiently. However, as the distance between the photo-taking lens optical system and the film exposure position is increased, the dimensions of the camera are proportionally increased, resulting in a camera so large that it is inconvenient to carry. In order to solve this problem, in the instant photographic camera, a front housing in which the photo-taking lens optical system is arranged and a rear housing in which the film exposure position is provided are formed separately, and connected with each other by an expandable bellows. When photography is performed, the bellows is expanded with the front housing and the rear housing being separated from each other to such an extent that the photo-taking lens optical system and the film exposure position are held at a suitable distance. Conversely, when in carrying without performing photography, the bellows is compressed so that the front housing and the rear housing are brought into intimate contact with each other, thereby making the camera compact and easy to carry. This kind of instant photographic camera has a complicated mechanism for assuring the accuracy of the distance between the front housing and the rear housing when photographs are being taken. And, as a method of facilitating the compactness of the camera without using the above mentioned complicated folding mechanism, it is known to arrange a plurality of reflection mirrors between the photo-taking lens optical system and the film exposure position to cause an image bearing beam of light rays passing through the photo-taking lens optical system to be successively deflected by the plurality of reflection mirrors in a zigzag manner, thereby reducing the distance between the photo-taking lens optical system and the film exposure position to provide a compact camera while eliminating the necessity for folding. In this type of instant photographic camera, because of the lack of the folding mechanism, the structure can be simplified, and, because of the normally fixed distance between the photo-taking lens optical system and the film exposure position it is possible to obtain a camera of extremely high precision. However, such type of photographic camera in which a plurality of reflection mirrors are arranged between the photo-taking lens optical system and the film exposure position to cause successive deflections of the image bearing beam entering through the photo-taking lens optical system by the reflection mirrors in a zigzag manner gives rise to the problem that as the image bearing beam of light incident upon the exposure position from the photo-taking lens optical system is always directed thereto by the above mentioned reflection mirrors, when dust and the like are deposited on said reflection mirrors, an important influence is exerted on photography. In other words, when dust and the like adhere to the reflection mirrors, this dust is imaged into the film. For this reason, as soon as the photographer is aware of the fact that dust has adhered on the above mentioned reflection mirrors and the like, the dust must be removed. In order to remove this dust, a piece of cloth has to be inserted through the film insertion slot, or, if it is impossible, it is necessary to disassemble the camera. Thus, the removal of dust is very troublesome. And, the adhesion of dust to said reflection mirrors usually results when the film is inserted into the camera, thereby permitting the dust to enter from the film insertion slot and to adhere on the reflection mirrors.